Hammer v. Dagenhart is among the best known cases in the canon of constitutional law. It struck down the first federal child labor law on the grounds that Congress’s commerce power allowed it to prohibit the interstate shipment of harmful goods, like impure food and drugs, but not harmless goods, like the products of child labor. Withering criticism of the decision spread from Justice Holmes’s famous dissent to law reviews, treatises, casebooks, and constitutional law classes. For nearly a century the decision has been scorned as inconsistent with precedent, incoherent as policy, and driven solely by the Court’s reactionary commitment to a laissez faire economy. That critique has in turn supported two destructive ideas: that constitutional law is merely an expression of the ideological preferences of Supreme Court Justices and that those preferences are the only important drivers of constitutional development.

Creating Hammer v. Dagenhart contributes to the growing critique of both those assertions by demonstrating that our conventional understanding of the Hammer doctrine is wrong in three ways: it underestimates the doctrine’s consistency with precedent, profoundly mischaracterizes the policies that supported the doctrine, and ignores the crucial influence of lawyers outside the courts. My research supports those claims by looking beyond the opinion itself and papers of the Justices, which reveal little about the forces that produced the doctrine. I instead recover the political, legal, and ideological origins of Hammer by examining the activities and ideas of the lawyer who can fairly be said to have created the doctrine: Philander Chase Knox. For more than a decade, Knox worked as Attorney General, Senator, and Presidential candidate to create, propagate and defend what became the Hammer doctrine. And the architect of the Hammer doctrine, it turns out, was no laissez faire zealot. He was instead a constitutional moderate who hoped the doctrine would preserve constitutional protection for traditional nineteenth century values while allowing Congress to address collective action problems generated by the increasing integration of the national economy.